Close #504 Add About Widget to configuration tool

Add AboutWidget to the left hand tree on the config tool. This
widget is based off the previous AboutDialog. It contains information
about Freeseer, including copyright and version. There are also three
buttons, one links the user to the freeseer read the docs page
for help, the second other lets them report an issue on github and
the third button links to the contact page on read the docs.

The AboutDialog has also been modified. Essentially it was converted
to a widget (AboutWidget), which is used now for both AboutDialog and
the config tool.

Related to #411
Fix #444 Separate recording logic from the concept of a talk/presentation

- Add metadata parameter to load_backend function in Multimedia
- Disable Record button and set tool tip when no presentations are available
- Prepare record_name and metadata in RecordingController and add
  extension to file name in Multimedia
- Split RecordingController load_backend function into two functions: one
  accepting a filename, one accepting a presentation
- Change RecordApp to call load_backend_with_presentation
- Change convenience commands to call load_backend functions from
  RecordingController